Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/tools/pki/ea_response.hpp

@@ -0,0 +1,47 @@
+#pragma once
+
+#include "certificate.hpp"
+#include "response_codes.hpp"
+#include <vanetza/common/byte_buffer.hpp>
+#include <boost/optional/optional.hpp>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class SecurityModule;
+
+/**
+ * \brief Decoded view of an InnerEcResponse payload.
+ * \see TS 102 941 §6.2.3.2.2
+ */
+struct EnrolmentResponse
+{
+    EnrolmentResponseCode code; // EA's responseCode; parsing succeeds for any value
+    ByteBuffer request_hash; // SHA-256 prefix of the matching request
+    boost::optional<Certificate> certificate; // new EC; present iff one was decoded — caller must still check `code == ok`
+};
+
+/**
+ * Parse a decrypted EnrolmentResponse per ETSI TS 102 941 §6.2.3.2.2.
+ *
+ * Verifies:
+ *   - outer Ieee1609Dot2Data is signedData
+ *   - signer = digest, matching HashedId8(ea_certificate)
+ *   - tbsData.headerInfo.psid == aid::SCR
+ *   - outer signature verifies against ea_certificate
+ *   - inner EtsiTs102941Data.version == v1
+ *   - inner content variant is enrolmentResponse
+ *
+ * For a non-ok responseCode the function returns normally and `code` holds it;
+ * `certificate` is populated iff the response actually contains one.
+ *
+ * \throws DecodingFailure on structural failure
+ * \throws VerificationFailure on signer-digest or signature mismatch
+ */
+EnrolmentResponse parse_enrolment_response(SecurityModule& security, const ByteBuffer& decrypted,
+    const Certificate& ea_certificate);
+
+} // namespace pki
+} // namespace vanetza